The invention relates generally to the field of digital computer systems and more particularly to a digital data storage subsystem including a directory for efficiently providing formatting information for records stored by the digital data storage subsystem.
In modern xe2x80x9centerprisexe2x80x9d computing environments, that is, computer systems doe use in an office environment in a company, a number of personal computers, workstations, mini-computers and mainframe computers, along with other devices such as large mass storage subsystems, network printers and interfaces to the public telephony system, may be interconnected to provide an integrated environment in which information may be shared among users in the company. Typically, users may be performing a variety of operations, including order receipt, manufacturing, shipping, billing, inventory control, and other operations, in which sharing of data on a real-time basis may provide a significant advantage over, for example, maintaining separate records and attempting to later reconcile them. The users may operate on their own data, which they may maintain on the computers they are using, or alternatively they may share data through the large mass storage subsystems.
One such large mass storage subsystem is described in, for example, U.S. Pat. No. 5,206,939, entitled System And Method For Disk Mapping And Data Retrieval, issued Apr. 27, 1993, to Moshe Yanai, et al (hereinafter, xe2x80x9cthe ""939 patentxe2x80x9d), and U.S. Pat. No. 5,381,539, entitled xe2x80x9cSystem And Method For Dynamically Controlling Cache Management,xe2x80x9d issued Jan. 10, 1995, to Moshe Yanai, et al., both of which are assigned to the assignee of the present invention and incorporated herein by reference. That patent and those applications generally describe an arrangement which allows data, as used by computers, organized in records, with each record being in well-known xe2x80x9cCKDxe2x80x9d (xe2x80x9ccount-key-dataxe2x80x9d) format, to be stored in storage devices which provide a xe2x80x9cfixed blockxe2x80x9d storage architecture. In this arrangement, a large cache is used to buffer data that is transferred from the storage devices for use by the respective computers, and, if the data has been modified, transferred back to the storage devices for storage.
In the systems described in the aforementioned patent and patent applications, a directory table is used to provide information concerning the data that is stored in the mass storage subsystem. In one embodiment, in which the mass storage subsystem stores data on a number disk storage devices, the table includes information concerning selected characteristics of each of the CKD records stored in the mass storage subsystem, organized by device, cylinder and read/write head or track, and includes such information as record size and certain formatting characteristics. The amount of data that can be stored by individual storage devices is continually increasing over time, both in terms of the number of cylinders that each device can store and in the amount of data each track can store, and so the amount of information which such tables needs to store can become quite large. U.S. Pat. No. 6,029,229, entitled xe2x80x9cDigital Data Storage Subsystem Including Directory For Efficiently Providing Formatting Information For Stored Records,xe2x80x9d issued Feb. 22, 2000, in the name of Natan Vishlitzky, assigned to the assignee of the present invention and incorporated herein by reference, describes a directory table in which the amount of information required for the various records can be advantageously reduced; however, it would be helpful to further reduce the size of the directory table.
The invention provides a new and improved digital data storage subsystem including a directory for efficiently providing formatting information for records stored by the digital data storage subsystem.
In brief summary, the invention in one aspect provides a digital data storage system comprising at least one storage device, a descriptor memory and a control device. The at least one storage device is configured to store a series of records, the records being organized in a plurality of tracks, each track being associated with one of a plurality of cylinders. The descriptor memory is configured to store at least one descriptor associated with the at least one storage device. The at least one descriptor contains selected information relating to the records stored by the at least one storage device. Each descriptor includes a plurality of cylinder portions each configured to store selected information relating to a respective one of the cylinders in the at least one storage device. Each cylinder portion, in turn, includes a plurality of track descriptors each configured to store selected information relating to a respective one of the tracks in the respective cylinder. The at least one storage device is further configured to store the at least one descriptor associated therewith, the cylinder portions of the at least one descriptor being augmented with additional information relating to the respective ones of the cylinders. The digital data storage system further includes a control device configured to use the at least one descriptor in connection with accesses of records in the at least one storage device.
In one embodiment, the additional information includes, for each cylinder, a cylinder identifier.